The present invention relates to an electro-optic modulation device and method of manufacture the same. More particularly, the present invention provides an improved process for forming a silicon-based waveguide used as one arm of a Mach-Zehnder Interferometer having a low Vpi PN junction with relaxing misalignment tolerance.
Over the last few decades, the use of communication networks exploded. In the early days Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was usually relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
Over the past, high data rate communication has been widely implemented via optical network, in which data signals are carried by laser light that is specifically modulated using various kinds of electro-optic modulators. As a key component in the silicon-based photonic integrated circuits for chip-scale high-speed data communication, Mach-Zehnder Interferometer (MZI) based modulator offers high modulation speed and low power consumption. Each MZI is fabricated as a silicon waveguide having at least a PN junction in one optical path which is associated with a characteristic voltage Vpi. Vpi is a voltage required for a MZI modulator to switch from a maximum transmission to a minimum transmission with a π-phase shift. Naturally, a lower Vpi value is desired to reduce driving voltage swing and power consumption of the MZI modulator in the silicon photonic integrated circuits. A width of depletion region of the PN junction directly impacts the value of Vpi. Lowering the width of depletion region can lead to a reduction of the Vpi. In order to fabricate a PN junction of the MZI with narrow depletion region, other than controlling P or N impurity doping profile via implantation, controlling implant mask alignment would be critical. However, convention manufacture methods usually adopt separate N and P implant masks for performing doping process independently in an N region and a P region, which is susceptible to mask misalignment issues. Often, a higher Vpi value is resulted from these process variation and other production issues. For example, a 1V increase of Vpi due to the implant mask alignment variation during manufacture of the PN junction may be accepted, limiting a tolerance margin of error.